The thermal velocities for H and D at temperatures appropriate for Venus are 5 and 3. So, since Contributing to the escape of H and D is the lack of a magnetic field for Venus.
Unlike Earth, Venus has no magnetic field, probably because its slighly lower mass prevents it from having a solid inner core, and it is the continuing freezing of liquid iron from the outer core onto the inner core that generates energy heat is removed from something when it goes from liquid to solid that drives the geodynamo that generates our magnetic field.
And the lack of a magnetic field means that Venus has no protection from the solar wind, so the solar wind can strip atoms from the top of Venus' atmosphere. But where do the hydrogen isotopes come from? The terrestrial planets do not have free hydrogen molecules or atoms in their atmospheres and most likely never did.
Rocks on terrestrial planets do not contain hydrogen unless the hydrogen was derived from water. Of the gases or volatiles in the terrestrial planets atmospheres and hydrospheres, only methane CH 4 , ammonia NH 3 and water H 2 O contain hydrogen.
Since methane and ammonia are not abundant it is likely that water is the principal reservoir for hydrogen. Thus, we are led to conclude that Venus lost at least Now we imagine that Venus once had oceans and water vapor in the atmosphere.
Perhaps Venus was had an Earthlike environment, but without life:. It might have happened very gradually. Image Venus a long time back. The planet is nearly identical in size, mass, composition and distance from the Sun as the Earth.
It begins like the Earth with global oceans, with CO 2 dissolved in the oceans, with carbonate rocks forming at the bottoms of the oceans. Heat from the interior drives plate tectonics and volcanic activity, recycling carbon from the rocks to the atmosphere.
The big distinction is the temperature. The reason: it once had water. The relatively small distance that separates Venus' and Earth's proximity to the sun makes a very big difference in temperature. Light falls off exponentially with distance, so a planet that is, say, twice as close to the sun as Earth is would get much more than twice the solar energy. Making problems much worse for Venus, its atmosphere is a thermal quilt, 93 times denser than Earth's and made up mostly of carbon dioxide and sulfur dioxide.
It might even help by pointing the way towards evidence of past life or some that still exists! Her faculty opponent was Dr. Further Reading: IRF. Currently, there is a lot of interest in understanding the difference between the escape rates at Venus, Earth and Mars. Skip to content. Like this: Like Loading Venus is roughly the same size and mass as Earth and even had plate tectonics. The sun was also dimmer during that epoch, so Venus, despite being closer to the sun than Earth is, was in the habitable zone, or the region where a rocky planet could have liquid water on its surface.
Some scientists suggest that habitability vanished when the sun's radiation grew stronger , causing the Venusian oceans to evaporate and water molecules to be thrown into the atmosphere.
Water vapor is a greenhouse gas that would have made it harder for heat to escape from the planet. The wet atmosphere began a cycle of rising temperatures, evaporating oceans and increasing water vapor that made temperatures rise even further. In September, researchers from NASA's Goddard Institute for Space Studies released simulations of several scenarios that would allow liquid water to exist at the surface for millions of years , before this runaway effect occurred.
But the new study suggests that such water oceans were never there in the first place.
0コメント